Section: New Results

Flexible Radio Front-End

The last decades have been really hungry in new ways to reduce energy consumption. That is especially true when talking about wireless sensor networks in general and home multimedia networks in particular, since electrical energy consumption is the bottleneck of the network. One of the most energy-consuming functional block of an equipment is the radio front end, and methods to switch it off during the time intervals where it is not active must be implemented. This previous study has proposed a wake-up radio circuit which is capable of both addressing and waking up not only a more efficient but also more energy-consuming radio front end. By using a frequency footprint to differentiate each sensor, awaking all the sensors except for the one of interest is avoided. The particularity of the proposed wake-up receiver [22] is that the decision is taken in the radio-frequency part and no baseband treatment is needed. The global evaluation in theory and in simulation was performed, and a first testbed of this technology was fabricated, demonstrating that this principle actually works in practice [21].

An important work was done in this axis previously around Full-Duplex systems, in order to enhance throughput, flexibility, and, potentially security of wireless links. A PhD thesis grant from DGA and Inria has allowed us to extend this through a collaboration with axis 2, focusing on Physical layer security mechanisms based on Full-Duplex systems. Starting by a theoretical study of the secrecy capacity in the presence of an eavesdropper, this work studies [13] the duality between wiretap channels and state-dependent channels. This represents a basic framework to extend in a near future this study to Full-Duplex scenarios, where the Full-Duplex capability of a node could increase the secrecy of the wireless communication.

The technologies employed in urban sensor networks are permanently evolving, and thus the gateways of these networks have to be regularly upgraded. The existing method to do so is to stack-up receivers dedicated to one communication protocol. However, this implies to have to replace the gateway every time a new protocol is added to the network. A more practical way to do this is to perform a digitization of the full band and to perform digitally the signal processing, as done in Software-Defined Radio (SDR). The main hard point in doing this is the dynamic range of the signals: indeed the signals are emitted with very different features because of the various propagation conditions. It has been proved that the difference of power between two signals can be so important that no existing Analog-to-Digital Converter (ADC) is able to properly digitize the signals. We propose a solution to reduce the dynamic range of signals before digital conversion. In this study [9], the assumption is made that there is one strong signal, and several weak signals. This assumption is made from the existing urban sensor networks topology. A receiver architecture with two branches is proposed with a “Coarse Digitization Path” (CDP) and a “Fine Digitization Path” (FDP). The CDP allows to digitize the strong signal and to get data on it that is used to reconfigure the FDP. The FDP then uses a notch filter to attenuate the strong signal (and then to reduce the dynamic range of the signals) and digitizes the rest of the band.